This invention relates to tufting machines, and more particularly to means for moving the needle bar of a tufting machine longitudinally of itself so as to provide a patterning effect in the tufted fabric being produced.
Such patterning means, generally referred to as needle shifting or stitch placement drives, conventionally fall into two categories. The first category is that of the cam driven type whereby a rotating plate cam, driven directly from the machine mainshaft, is drivingly engaged with the needle bar so as to effect the required displacement thereof. The second category is that of the progammable type which may be hydraulically or pneumatically driven, or driven mechanically through some form of programmable indexing device whereby a ram is drivingly engaged with the needle bar so as to effect the required displacement thereof. Examples of such drives are illustrated in U.S. Pat. Nos. 4,173,192 and 4,010,700, and U.S. application Ser. No. 245,377 filed Mar. 19, 1981.
The cam driven type has the advantage of being simple, inexpensive and reliable. With this type breakdowns are infrequent and repair is easily and speedily effected when required. However, in order to produce tufted fabrics of differing patterns it is necessary to provide differing cams and to change cams when a pattern change is required. Consequently, it is impractical to conduct sampling trials for differing new designs since an appropriate cam is required for each pattern variation being considered.
The hydraulically, pneumatically and mechanically indexed types are more complex and costly than the cam driven types and are more prone to breakage and malfunctions. Maintenance and repair is complex and time consuming and for these reasons many carpet manufacturers prefer to use cam driven machines. However, the programmable types have the advantage that their programs may be readily changed so as to provide differing patterns of tufted fabric. As a consequence if a carpet manufacturer wishes to conduct sampling trials with differing new designs he must either purchase a machine having such a programmable needle bar traverse mechanism or buy time on such a machine belonging to another carpet manufacturer or tufting machine manufacturer.